1. Field of the Invention
The present invention relates to a developing unit of an image forming apparatus, and more particularly, to a non-contact type developing unit of an image forming apparatus using a single-component nonmagnetic toner.
2. Description of the Related Art
In a non-contact developing unit using a single-component nonmagnetic toner, it is typically required to maintain a regular gap (hereinafter, called ‘developing gap’) between a photoconductive drum and a developing roller. In addition, the developing roller is typically driven by a driving force transmitted from a photoconductive drum gear of the photoconductive drum to a developing roller gear of the developing roller. At this point, a developing gap irregularity is often caused by a repulsive force generated in a pressure angle α direction, as shown in FIGS. 1 to 3. Such an irregular developing gap has a severe influence on the image quality, and therefore, close maintenance of the regular developing gap is required.
One conventional way of maintaining the regular developing gap is by a developing unit as shown in FIG. 1.
According to FIG. 1, an example of a conventional developing unit 1 comprises a photoconductive part 20 and a developing part 40. The photoconductive part 20 includes a first support body 10, an electrifying roller 11 provided in the first support body, a photoconductive drum 12, a cleaning blade 13 and a waste toner tub 14. The developing part 40 includes a second support body 30, a developing roller 31 provided in the second support body 30, a controlling blade 32, a toner supplying roller 33 and a toner 34. The developing unit 1 further comprises a positioning member 50 which is included in the developing part 40 and rotatably supported by the photoconductive part 20 to determine a position of the developing roller 31 with respect to the photoconductive drum 12.
The above-structured developing unit 1 develops an electrostatic latent image on the photoconductive drum 12 as described in greater detail below. A driving force is transmitted from a main body of the image forming apparatus to the photoconductive drum gear (not shown) of the photoconductive drum 12, and transmitted from the photoconductive drum gear to the developing roller gear (not shown) of the developing roller 31. Also, the driving force is transmitted to a gear (not shown) of the toner supplying roller 33 via an idle gear (not shown), and thereby the photoconductive drum 12, the developing roller 31, and the toner supplying roller 33 are rotatably driven. Thus the electrostatic latent image is developed.
Here, in order to prevent the developing gap irregularity by the repulsive force generated in the pressure angle α occurring in the driving force transmitting process, the rotation point 51 of the positioning member 50 is placed on the pressure angle α vector, as shown in FIG. 1, thereby pressing the developing roller 31 to the photoconductive drum 12.
However, the conventional method of maintaining the developing gap by controlling only the rotation point 51 of the positioning member 50 has a difficulty in managing parts, since to function properly, the parts should be fabricated with high precision for providing the regular developing gap. In particular, a compact-sized developing unit is difficult to realize due to restrictions in determining the rotation point 51.
FIG. 2 is a sectional view illustrating another conventional method for maintaining the regular developing gap. In referring to the elements having the same structure and operation as shown in FIG. 1, the elements will be cited by the same reference numerals and detailed description thereof will be omitted.
According to FIG. 2, in a developing unit 2, a rotation point 51A of a positioning member 50A is placed in a predetermined range β and a moment 91 is applied to press the developing roller 31 against the photoconductive drum 12 using a separate pressing member (not shown) to prevent the developing gap irregularity from occurring by the repulsive force generated in the pressure angle α of the gear during the transmission of the driving force.
The above conventional method maintains the regular developing gap of the developing roller 31 with respect to the photoconductive drum 12 by using the moment 91 obtained via a pressing member as well as controlling the rotation point 51A of the positioning member 50A. However, there are still problems, such as variation of a driving load according to toner quantity and usage. It is also difficult to plan for the pressing member considering both a tolerance of part size and assembly deviation. Therefore even in this approach, it is difficult to maintain a certain quality.
FIG. 3 is a sectional view of a developing unit for illustrating yet another conventional method of maintaining the regular developing gap. Again, the elements of the same structure of FIGS. 1 and 2 will be referred by the same reference numerals, and the description thereof are omitted.
Referring to FIG. 3, in a developing unit 3, a positioning member 50B is provided in a gravity-direction positioning member 15 which is mounted in the first support body 10 of the photoconductive part 20 to determine a first gravity-direction position. A member 60 is mounted in the main body of the image forming apparatus to determine a second gravity-direction position of the developing part 40.
In the above developing unit 3, to prevent the developing gap irregularity due to the repulsive force generated in a direction of the pressure angle α of the gear, positions of the positioning member 50B and the developing roller 31 are determined during transfer of the driving force. Specifically, the position of the positioning member 50B for determining the first gravity-direction position of the developing part 40 from the gravity-direction positioning member 15, and the developing roller 31 with respect to the photoconductive drum 12 to the second gravity-direction positioning member 60, are both determined during transfer of the driving force. Then, the moment 92 is applied to press the developing roller 31 against the photoconductive drum 12 using the separate pressing member (not shown).
However, the above method for maintaining the regular developing gap has similar problems as the developing unit 2 of FIG. 2, that is, it is difficult to design the pressing member while considering the variations of a driving load according to quantity and usage of the toner 34, including both parts size deviation and an assembly deviation. It is also hard to maintain quality of the pressing member at a certain level.
Accordingly, a need exists for a non-contact type developing unit of an image forming apparatus using a simple component to address the problems described above.